1. Field of the Invention
The present invention relates to an image building apparatus and more particularly to improvement of or relating to an image building apparatus for building color image on material to be image transferred by transfering thereto a plurality of coloring agents on thermal transfer material by means of a printing head while the material to be image transferred is reciprocably displaced at every time when one color has been thermally transferred with the material to be image transferred and the thermal transfer material interposed between the printing head the platen roller in the juxtaposed state.
2. Description of the Prior Art
A heat sensitive transfer recording apparatus will be called as one of the above-mentioned type of apparatuses. The heat sensitive recording apparatus is typically constructed such that color image is built on material to be image transferred (printing medium) by transferring thereto a plurality of coloring agents on transfer material (thermal transfer ribbon) by means of a thermal head while material to be image transferred is reciprocably transported round a platen. When transference is effected, material to be image transferred and transfer material are caused to move through the space as defined between the thermal head and the platen while they are held in the juxtaposed state. At every time when one coloring agent having a certain color has been transferred onto material to be image transferred, they are reciprocably displaced and transferring operations as mentioned above are repeated until a predetermined number of coloring agents are transferred thereto.
However, it is often found with respect to the hitherto known apparatus as described above that such a malfunction as dislocation of color transference takes place at every time when transference of coloring agent having one color is shifted to that of coloring agent having another color while material to be image transferred is reciprocably displaced. This is attributable due to slippage of material to be image transferred on the surface of the platen. To obviate the foregoing problem there was already made a proposal that a pair of thrust rollers are disposed at the position located before and behind the thermal head as seen in the direction of transportation of material to be image transferred in order to assure that material to be image transferred is reciprocably displaced while it is normally clamped between the thrust rollers and the platen.
However, the proposed conventional apparatus has a problem that an area where no image is built on material to be image transferred (both the end parts of material to be image transferred as seen in the direction of transportation of the same) increases, because arrangement is so made that material to be image transferred is reciprocably displaced during color transfering operation whle it is normally clamped between the thrust rollers and the platen.
Further, to assure that material to be image transferred is properly brought to the thrust rollers along the peripheral surface of the platen after it passes through the space as defined between the platen and the thermal head there was made another proposal that the conventional apparatus is provided with a pair of thermal transfer material guide members which are projected toward the platen in the area located between the pair of thrust rollers and thereby transfer material is brought in thrust contact with a part of the peripheral surface of the platen while it is kept in the stretched state by means of the pair of guide members.
In practice, there are raised the following requirements for guide members of the above-mentioned type.
(1) To assure that material to be image transferred is smoothly displaced in the area between the thrust rollers it is preferable that a winding angle of transfer material relative to the platen is determined as large as possible while it is brought in close contact with the peripheral surface of the platen.
(2) The conventional apparatus is not provided with any member in the area located between the thrust rollers and the guide member by means of which material to be image transferred is thrusted against the platen. For the reason it is preferable that the above-mentioned area has a length as short as possible from the veiwpoint of inhibiting an occurrence of dislocation of color transference due to slackening of material to be image transferred in the area.
(3) It is preferable that a distance between the platen and the guide member is determined to such a value that there does not take place malfunction such as slackening of material to be image transferred, clogging of the latter or the like.
In view of the above-mentioned requirements the positional relation of the guide members relative to the platen is a very important thing. It should be noted that this positional relation should not limitatively applied only to the thermal head and thing is same with other type of printing head.
When monochromatic image or multicolor image is built on material to be image transferred by using a thermal head, coloring agent on transfer material is molten under the influence of elevated temperature generated by a number of heating resistors on the thermal head and thus molten coloring agent is then transferred onto material to be image transferred. With respect to the heating resistors it is required that they are arranged in parallel with the axis of the platen and moreover they come in uniform contact with the part where thrust force of the thermal head to be exerted on the platen is maximized . Accordingly, since the positional relation between the platen and the guide member is an important thing as described above, the positional relation of the guide members relative to the heating resistors on the thermal head is also an important thing from the viewpoint of meeting the above-mentioned requirements.
However, the conventional apparatus as descrived above has problems that it is difficult to adjustably locate the position of components constituting the apparatus during manufacturing or at a time of maintaining service and there takes place fluctuation in relative positional accuracy among the components, resulting in operational reliability of the apparatus being reduced.